A new, unconventional cutting strategy, Hybrid Machining, has been developed by Vero Software that give users benefits with their existing machining equipment. It is particularly relevant to the processing of difficult-to-machine materials, as Massimo Vergerio, CAM product manager, VISI, explains
Difficult-to-machine materials, such as tough super alloys, titanium, ceramics and composites, together with design requirements for precise complex shapes and fine surface finishes are challenges that drive rising machining costs.
Advanced materials play an increasingly important role in modern manufacturing industries, especially aircraft, automotive, tool, and die and mould making. They boast greatly improved mechanical properties, such as greater strength, and resistance to heat, wear and corrosion, have enormous economic benefits through improved product performance and design. But they present a challenge that sees traditional cutting strategies unable to tackle them economically or, in some cases, to machine them at all.
To meet the challenge, the VISI product management tasked its research and development team to define a new cutting strategy.
Months of analysis and real-life trials, in collaboration with leading cutting machine research centres, proved that technological improvements to the machining process could be achieved by combining different mechanical actions derived from existing standard cutting strategies.
VISI calls its new unconventional cutting strategy Hybrid Machining, or HM. It uses combined or mutually enhanced advantages of two or more conventional cutting strategies, avoiding or reducing most of the adverse results these processes could produce when applied individually.
With VISI and HM, there are almost no limits in combining standard cutting strategies, with their individual advantages, to create new toolpaths that intelligently adapt the shape of their motions according to the shape of the workpiece.
This new toolpath characteristic gives a number of advantages every time the process is used:
• Enhanced stock management
• Shorter cutting path length
• Sensible reduction of rapid movements
• Shorter overall toolpath length
• Better toolpath quality
• Longer tool life
• Overall cost saving
HM is now a fundamental technology within VISI and is used by thousands of manufacturers worldwide. HM Roughing was the first available command offering this technology and remains one of the most interesting applications of this approach.
Traditional roughing strategies are designed to remove material as fast as possible while leaving a stock allowance. These traditional strategies generally need large tools and require the definition of a generic starting stock – typically cuboids or cylinders. The technological approach consists of slicing the work piece and stock at a given Z increment (step down) and to pocket in/out at each level with a given pass offset (stepover). To guarantee complete material removal for each slice, the stepover is typically slightly lower or slightly above 50% of the tool cutting diameter.
In recent years, trochoidal toolpath motions have been offered as an alternative solution for roughing. But even although this technology provides a number of advantages over standard roughing – in particular on hard materials – it is also the case that, for many manufacturers, the necessary investment to fully benefit from this technology, such as high speed machines and special tools, as well as changing their working habits, cannot always be justified.
HM roughing, de-facto, is the perfect fit between the standard approach and the trochoidal solution, allowing most manufacturers to push the boundaries of their existing technology, without requiring additional investments, additional costs, or having to learn a new method. It means material can be cut faster by machining only where necessary (fully stock based), that stepover values can be almost the complete cutting diameter of the tool, without generating leftover or un-cut areas, while toolpath motions are morphed to maintained peripheral speed and reducing tool wear. Additional, fully smoothed hybrid motions are automatically inserted in critical areas, and both new and old machining centres can exploit, fully, their specific limits.
A key point is that HM roughing accurately controls and adds the toolpath motions only where the stock material exists, including undercut areas or during a multi-axis repositioning (a 3 + 2 solution where the same work piece is machined from multiple directions). This technology alone, massively reduces the machining time whilst ensuring complete material removal.
Highlights of this innovative technology include:
• Hybrid spiral motions: Optimised pocket toolpath, avoiding vertical plunging wherever possible. Image: HM Sprial
• Fully stock based and volume awareness: Stock shape and volume are fully considered while creating a fluent toolpath that allows higher speed machining and less rapids. Image: Stock based
• Extreme stepover management: HM roughing introduces an innovative offset algorithm allowing the use of extremely large stepover values, while still ensuring complete material removal and a high speed toolpath. The toolpath created is not only more effective, but it also preserves tool life. Image: Stepover management
• Intermediate plane management: Flat areas between successive slices are also manageable, avoiding the possibility of leaving the part with uneven stock allowance. Image: Plane management
• Vertical corner management: The use of a large tool in roughing can leave large chunks of un-machined material, mostly on vertical corners where the largest diameter of the tool comes into play. With HM roughing it is possible to automatically reduce the material on those areas with a second operation using a smaller tool. Image: Corner machining
• Convex tip tool management: Convex tool types are extremely effective for roughing operations, and VISI's Hybrid Machining provides the ability to fully benefit from their use Image: Convex Tip
The following three examples highlight the benefits that manufacturers have gained from using Hybrid Machining:
Case study 1: Machining a part of 250 by 130 by 74 mm (X, Y, Z) with a 20 mm diameter tool:
Feed length (metres) 392.19 (traditional roughing, spiral); 266.92 (HM roughing, sprial); advantage = 32%
Rapid length (metres) 8.47 (traditional roughing, spiral) 5.28 (HM roughing, sprial), advantage= 38%
Total length (metres) 400.66 (traditional roughing, spiral); 272.20 (HM roughing, sprial); advantage=32%
Feed time (mins: secs) 53:31 (traditional roughing, spiral); 36:57 (HM roughing, sprial); advantage= 31%
Rapid time (mins: secs) 01:03 (traditional roughing, spiral); 00:39 (HM roughing, sprial); advantage= 38%
Total time: (mins: secs) 54:35 (traditional roughing, spiral); 37:37 (HM roughing, sprial); advantage= 31%
Image: Case study 1
Case study 2: Machining a part of 113 by 113 by 95 mm (X, Y, Z) with a 12 mm diameter tool:
Feed length (metres) 241.70 (traditional roughing, spiral); 37.78 (HM roughing, sprial); advantage=85%
Rapid length (metres) 162.25 (traditional roughing, spiral); 33.59 (HM roughing, sprial); advantage=79%
Total length (metres) 403.94 (traditional roughing, spiral); 69.38 (HM roughing, sprial); advantage=83%
Feed time (mins: secs) 36:37 (traditional roughing, spiral); 05:25 (HM roughing, sprial); advantage=85%
Rapid time (mins: secs) 16:13 (traditional roughing, spiral); 03:21 (HM roughing, sprial); advantage=79%
Total time: (mins: secs) 52:50 (traditional roughing, spiral); 08:46 (HM roughing, sprial); advantage=83%
Image: Case study 2
Case study 3: Machining a part of 253 by 200 by 207 mm (X, Y, Z) with a 32 mm diameter tool:
Feed length (metres) 369.14 (traditional roughing, spiral); 348.31 (HM roughing, sprial); advantage= 7%
Rapid length (metres) 45.88 (traditional roughing, spiral); 13.64 (HM roughing, sprial); advantage=70%
Total length (metres) 415.02 (traditional roughing, spiral); 361.94 (HM roughing, sprial); advantage=24%
Feed time (mins: secs) 39:48 (traditional roughing, spiral); 37:45 (HM roughing, sprial); advantage=5%
Rapid time (mins: secs) 04:05 (traditional roughing, spiral); 01:12 (HM roughing, sprial); advantage=71%
Total time: (mins: secs) 43:53 (traditional roughing, spiral); 38.58 (HM roughing, sprial); advantage=15%
Image: Case study 3